Infection by Streptococcus pneumoniae is the most frequent opportunistic infection observed in HIV-infected children. PCVs are immunogenic and efficacious in normal children and offer hope of reducing pneumococcal infections in HIV-infected children. The degree to which children on HAART are protected by prior immunizations and are responsive to new immunizations is still largely undefined. This study is designed to answer whether PCV immunizations are safe and effective. The immune responses to prior immunizations and responsiveness to booster doses of vaccines against measles, pertussis, and hepatitis B virus of children on HAART will also be examined. Answers to these questions will determine whether these children are likely to be protected against these clinically relevant pathogens and whether they should routinely receive booster doses of these vaccines after a period of HAART.